The present invention relates to communication processing methods in a cluster communication system, and more particularly to a communication processing method which can perform management of terminal management information efficiently and an apparatus therefor.
In a cluster communication system in the prior art, as disclosed in Japanese patent application laid-open No. 60-160750, a terminal controller performs communication control for each terminal device according to a communication control using a polling command. In this communication control system, the terminal controller and each terminal device respectively have their own pieces of information, and only the apparatus having the address contained in the transmission data can receive the data. The terminal controller transmits a frame which represents an invitation to send, called a polling frame, to each terminal device. A terminal device which receives this frame, that is, only a terminal device having the address contained within the frame, is allowed transmission of a data frame transmitted by the terminal controller or other terminal device. This is called acquisition of the right to send data.
In such a cluster communication system using communication control by polling command in the prior art, the terminal controller performs terminal management according to a terminal status management table which stores the status of each terminal device. The polling frame is transmitted in sequence corresponding to the content of this terminal status control table.
On the other hand, when each terminal device performs data transmission to the terminal controller or another terminal device, the following procedure is used. (1) The right to send data is acquired by polling, and (2) the transmission data is embedded in a frame having the destination station address and the frame is transmitted. (3) Response from the destination station is received, and (4) the right to send data is returned to the terminal controller. However, if there is no transmission data, items (2), (3) are omitted, and the right to send data is immediately returned.
In such a communication system, since each terminal device has means for determining the terminal status within the same cluster, when the destination station terminal is not ready for receiving data, a useless transmission, such as power source OFF or BUSY state, can be avoided. A method for each terminal device to determine the terminal state within the same cluster is as follows. In order that all terminal devices can receive the data frame commonly, a global address is provided, and every time the control of the terminal management table varies, the terminal controller transmits the terminal management table information to all terminal devices. In this way, each terminal device always can know the newest terminal management state of the same cluster, and a useless transmission is not repeated, or each time the transmission is performed, the state of the transmission destination terminal need not be indicated to the terminal controller, with the result that the line use efficiency is improved.
A system for performing data transmission to a number of terminal devices together is disclosed in Japanese patent application laid-open No. 57-101933.
In the cluster communication system, the terminal controller and each terminal device (hereinafter referred to as each communication processing system or each device) are usually provided with an adapter to perform communication control. In other words, if the main processor of each device undertakes all of the communication control, it is difficult for the device to attend to the performance of the communication processing. Consequently, it is usual for the communication control adapter installed on each device to perform communication processing for the lower level, for example, the data link level.
When each device is provided with information to control the terminal state in the cluster communication system, the information is stored in table form in the memory. In this case, the memory must be able to be accessed from both the main processor and the communication control adapter. That is, the terminal management table is mainly controlled by a program in the main processor. On the other hand, the communication control of the lower level is performed by the communication control adapter, and in order to improve the line use efficiency, the adapter must access the terminal management table and know the state of the destination station of a communication, and depending on the result, it must discriminate whether data should be transmitted or not. Consequently, a contention state for access from both the main processor and the communication control adapter to the terminal control table may be produced, resulting in deterioration of the communication control processing.